Source: \Dropbox\web\raspberry_pi\temperature_analysis\

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Water Temperature Measurements - Wareham and Poole Harbour 2021-06-14

Sample Measurements

A one way, tide assisted trip from Wareham down the River Frome to Poole Harbour, looping around the Arne Penisnsula and around Long and Round Islands to Brownsea Island and finishing with a crossing to Shell Bay.

Temperature measurements were made from two kayaks. There had been a hot spell over the previous days and the trip was undertaken under full sun with the air temperature in the low 30s.

Poole Harbour is mostly very shallow - some estimates place the average water depth at about 48 cms. The chart below shows the main shipping channels in white, and areas which are normally covered by water in blue. The green areas are uncovered during low tides.

At some parts of the tidal cycle Poole Harbour experiences a double high tide. On this day the main high tide was at 11:40 UTC with a second high around 15:00 UTC.

The trip was undertaken a few days after a weak Spring Tide; the tidal range was just 0.7 m.

Trip Timings

  A     10:30 UTC     leave Wareham on River Frome  
  B     11:15 UTC     leave River Frome; join Poole Harbour  
  -     11:40 UTC     High Tide  
  C     11:45 UTC     arrive Turford (Arne Penisnsula)  
  D     12:15 UTC     leave Turford  
  E     13:05 UTC     arrive Shipstal (Arne Penisnsula)  
  F     13:40 UTC     leave Shipstal  
  G     14:25 UTC     brief stop near Old Brownsea Island Pottery  
  H     15:05 UTC     arrive Brownsea Castle  
  I     15:50 UTC     leave Brownsea Castle  
  J     16:05 UTC     arrive Shell Bay  

Time Series

Temperature measurements were made from both kayaks.

The graph below shows a time series of temperature measurements (vertical axis) from both kayaks covering the whole period of the trip (horizontal axis). The gaps in the graph correspond to times when the kayaks were out of the water.

    Click image below for full size graph

Starting at Wareham [A] the river temperature was 17.4°C, moving downstream the temperature increased slowly to 19.5°C and when the river opened out into Poole Harbour [B] the temperature increased rapidly to between 22 and 23°C;.

These relatively high temperatures were maintained until the eastern end of Brownsea Island and the deep ship channel to the Harbour Entrance. Near the shallow, sheltered landing at Shell Bay the temperatures increased again.


By combining these temperature-time measurements with position-time information from a GPS the location of each temperature measurement can be determined. These values can then be plotted on an interactive map.

In the maps below measurements from both kayaks/sensors are presented as colour coded circles with whites and greens being cold, and reds and purples being warm. By clicking on a circle the actual measurements can be examined.

Wareham Public Slip

River Frome just below Wareham

Turford Beach on the Arne peninsula

Shipstal Point looking across to Long and Round Islands

Landing Stage on Round Island

Some of the highest water temperatures were encountered between the Arne Peninsula and Long and Round Islands.

The warm water seemed to suit at least one seal.

Cliffs on Southern Shore of Brownsea Island

Approaching Brownsea Castle

Big Ferry in the Main Channel